US2457550A - Condensing zinc vapor - Google Patents

Description

Dec. 28, 1948. 2,457,550

3. T. MAHLER .ETAL

CONDENSING ZINC VAPOR 4 sheet-sheet 1 Filed March 11, 1948.

GEORGE I MAME/:f E'Rw/N HAN@ WER/ nd?, M, M

ATTORN EY5 Def?. 28, 1948.

G; T. MAHLER ETAL CONDENSING ZINC VAPOR 4 Sheets-Sheet, 2

Filed March 11, 1948 INVENTORS SORGE IMA HLE@ ATTO RNEYS 135528, 194s. Q f, MAHLER ETAL. 2,457,550

CONDENSING ZINC VATOR Filed MarOh 11, 1948 4 Sheets-Sheet 3 lNvEN-roRs /5 Y GEORGE Ima/fw@ H r l H r I Few/BQ HA/vpwemw ATTORNEYS Dec. 28, 1948.

Filed March 11, A i948 G. T. MAHLER ETAL 2,457,550

CONDENSING ZINC VAPOR 4 Sheets-Sheet 4 lNv'EN-roRs GFORGE 7.' MA H1. El? El? W//Y 61 A/a Man/ERK 72W." MM @im ATTORNEYS Patented Dec. 28, 1948 ooNDENsING ZINC VAPOR George T. Mahler, Palmerton, and Erwin C.- Handwerk, Lehighton, Pa., assignors to The New Jersey Zinc Company, New York, N. Y., a corporation of New Jersey Application March 11, 1948, Serial No. 14,286

2 Claims. 'i

This invention relates to the condensation of zinc vapor and involves an improved method of condensing Zinc vapor.

The condensation of zinc vapor is beset by problems which are not encountered in the condensation of any other substance. Zinc vapor to be condensed is generally obtained in admixture with the gaseous products of a Zinc smelting operation consisting largely oi carbon monoxide at substantially the temperature prevailing in the zinc smelting operation. As the zinc vapor bearing gases are cooled in the course of condensation, carbon monoxide appears to undergo dissociation into carbon dioxide and carbon at approximately the boiling point temperature of zinc. Carbon dioxide at such an elevated temperature is an oxidizing agent for zinc. Accordingly, as the Zinc vapor condenses into the initial form of droplets, there is a pronounced tendency for theI surface of these droplets of molten metal to become oxidized by the carbon dioxide and to becomefurther contaminated by the iinely divided carbon produced by dissociation of the carbon monoxide. As a result, the surface of the droplets of molten zinc becomes so altered as to interfere with subsequent coalescence of the droplets to form a body of molten metal. vThe 'contaminated droplets remain in this form and solidify as dust-like particles known as blue powder,. Blue powder is not ordinarily salable and must be returned to the smelting operation for remelting.

The production of blue powder may be minimized by rapid cooling of the Zinc through the critical temperature range in which J carbon monoxide dissociates and exists in equilibrium with carbon dioxide. Excessively rapid cooling of zinc vapor through this critical range leads, however, to increased production of Zinc dust in a form known as physical blue powder. `It is generally believed that physical blue powder is formed by cooling the zinc so rapidly that droplets of condensed molten zinc are chilled to the solid state before they have had an opportunity to coalesce and form a body of molten metal. It

is apparent therefore that rapid cooling of zinc vapor in a condenser has certain limitations. The condensers used heretofore with modern externally-heated vertical zinc retorts, utilizing the most effective vcooling rate and other condensing conditions, commonly produced blue powder or zinc dust amounting to about 7% to 15 of the zinc output. l i.

The method of -the present invention makes possible the condensation of zincvapor with the formation within the condensing chamber of a relatively negligible amount of blue powder, generally in the neighborhood of 1% or less. The method of the inventionv is particularly adapted forV condensing zinc vapor diluted vnth ordinary smelting gases, such as carbon monoxide and the like, and is particularly adaptedfor use in condensing Zinc vapor from the smelting of zin=c by means of modern externally-heated vertical zinc retorts or electro-thermally heated retorts of large capacity, I

The method o'f condensing Zinc Vapor in accordance with the invention comprises throwing molten zinc outwardly from a plurality of vertically spaced points disposed within aclosed condensing chamber `or vessel and condensing the zinc vapor by passing it in a gaseous stream through the chamber in Contact with lthe shower of molten zinc. The molten zinc thrown into the condensing chamber is obtained inaccordance with theV invention by maintaining a body of molten zinc within the condensingchamber, raising molten zinc from the body thereof vertically within the chamber, and throwing the raised molten zincby Icentrifugal forceinto and throughout the chamber above the body of molten zinc therein in the form of an umbrella-like shower. The molten zinc is advantageouslyraised from the body of .molten metal within the condensing chamber bymeans of a rotating opentopped channel 'spirally disposedv about a substantially vertical axis within the chamber. The channel is rotated at a speed sulcientkto cause molten zinc therein to overiiow the channel by centrifugal Aaction andbethrown into thel chamber in sheets traveling at high velocity. The flying sheets of molten zinc oder a large surfaceuat a relatively low. temperature (of the order of 550 C.) for effecting the condensation of zinc vapor and for rapidly `coolingrthe gases -entering the condenser to the dewp'oint. The impact ofthe ying sheets of zinc upon any mist or droplets of zinc formed in the course of `condensation brings about rapid coalescenceof the mist and droplets with the molten Zinc.

'Ifhe apparatusused for condensing zinc vapor in accordance with the invention comprises a closed vessel or chamber having a, Zinc vapor in-f let and a gas outlet. A screw lift is disposed Vertically'within the vessel and is provided with a retaining wall capable of permitting radial discharg'etheretlrough of-molten Zinc raised by the lift; A The screw lift is adapted when rotated to raise molten zine from a body thereof in communic'ation with the lowerend of the lift. Means are provided for-rotating the lift soas to-rase stainless steel or the like, which extends longitudinally along the axis of the body member. The lower end of the shaft 28 is threaded to engage the threaded interior 21 of a fixed coupling plug 28 which is shown in detail in Fig. 6. The plug 28 is preferably a tapered body having a substantially square cross section and resembling a. truncated pyramid. The -plug 28 is screwed onto the threaded end of the shaft 26 and is locked in place by a tapered pin 3U extending through a transverse opening 3ldrilled through the plug. The -plug is seated in an opening 32 of substantially complementary shape machined in the lower end of the graphite body member 25. The depth of the opening 32 is such that the plug 28 is countersunk therein. A circular cut is also made in the end of the graphite body member 25 of slightly greater diameter than the maximum cross sectional dimension of the plug 28 and as deep as the extent of countersinking of this plug in the end of the body member. The resulting space, after the plug has been secured in position, is filled with a graphite paste 33, or the like, in order to completely cover the metal plug 28 and prevent contamination of the molten zinc by this metal.

The upper end of the screw lift is similarly coupled to the drive shaft 26 by an upper metal plug 34. The plug 34 is provided with an unthreaded central opening 35 of sufficient size to permit the plug to slide freely along the shaft 28. The opening 35 is provided with a keyway 36 adapted to engage a key 31 mounted longitudinally along the surface of the shaft 2S adjacent the upper end of the graphite shaft-like body member 25. The plug 34 may thus be slid over the upper end of the shaft 26 and moved into place in a complementary-shaped opening 38 in the upper end of the body member 25. In this position, the -plug becomes keyed to the screw lift and is also coupled to the shaft 26 by the key 31. The plug is held securely in position in the end of the lift by conventional means such as a washer 40, a nut 4| and a check nut 42 engaging threads on the shaft 26. As the nut 40 is tightened on the shaft, the two metal plugs v28 and 34 are forced toward one another and are firmly locked in coupling engagement within the ends of the screw lift. The two plugs are coupled to the shaft 2B by the tapered pin 30' in the lower plug 28 and by the key 31 engaging the upper plug 34.

As can be seen in Fig. 1, the screw lift 2l is suspended within the condensing chamber l on the end of the shaft 26. The upper portion of the body member 25 of the screw lift, on which the channel 22 is not formed, extends upwardly through an opening 43 in the roof of the condensing chamber. A tight seal between the condensing chamber and the body member 25 is insured by a packing gland 44 positioned within the roof opening 43. The size of the roof opening 43 is preferably such as to permit the screw lift 2| to be inserted into or removed from the condenser through this opening.

The drive shaft 26 is supported by twobearings 45 located above the condensing chamber l0. At least one, and preferably both, of the bearings 45 is a thrust bearing capable not only of supporting the weight of the screw lift 2l but also the weight of the molten zinc which is raised by the lift.

lThe thrust bearings are secured to supporting elements 46 which are either suspended from above the condenser or are mounted on the floor about the condenser.,

In this way, the weight of the screw lift in operation, and any vibration as'.- sociated with this operation, are not transmitted to the condenser structure. The drive shaft 26 is rotated by a pulley wheel 41, or the like, keyed to the upper end of the shaft. i

In operation, the screw lift functions as follows. 'Ihe lower most end of the channel 22 is immersed in the body of molten zinc within the condensing chamber. When the channel is rotated about its axis, by rotation of the drive shaft 26, the channel functions as a screw lift and raises molten zinc therein. The shaft 26, and hence the channel 22, is rotated at a sufiicient speed to cause centrifugal force to take over control of the molten zinc in the channel and to` cause this molten zinc to overflow the open tcp of the channel throughout a substantial portion of its length. The molten zinc is thus thrown out of the channel through the screw lift retaining wall provided by the outer side wall of the channel and is hurled toward the side walls of the condensing chamber. The upward motion of the zinc being raised by the channel is also imparted to the molten metal thrown outwardly therefrom and causes the metal to be thrown in a generally outward andupward direction into `the chamber. The molten metal is thrown from the channel throughout a substantial portion of its full lengt-h and thereby forms a continuous series of spiralling umbrella-like showers of molten zinc emanating from a plurality of points vertically distributed within the chamber. The molten metal thus thrown forcibly against the side walls of the chamber rebounds in all directions and effectively bathes the interior surfaces of the condenser with the molten metal thrown upwardly from the body of molten zinc in the bottom of the chamber,

YThe bathing of the inner surfaces of the condensing chamber by the relatively cool molten metal thrown thereagainst insures a cooling tempcrature substantially below the boiling point of zinc, but not below the melting point of zinc, on substantially all surfaces with which the incoming zinc vapor makes contact. The cooling effect of hea-t transfer through the walls of the condenser, whether effected solely bythe atmospheric air outside the chamber or by water-cooled jackets, is imparted to the molten metal which is constantly bathing these walls, but the presence of this molten metal on the walls prevents the .chilling of any zinc vapor within the chamber toa temperature below the melting point of zinc. The droplets of condensed zinc vapor are thus permitted adequate opportunity to coalesce, and this coalescence is promoted to an exceptional degree by the practically total pervasion of the 'chamber by molten zinc. The foregoing condi'- tions insure rapid cooling of the incoming carbon monoxide and zinc vapor through the critical temperature zone in which the carbon monoxide tends to dissociate and therebyrsubstantially preclude the development of an oxidizing atmosphere within the condensing chamber as the zinc vvaporis cooled to its dew point. In this way, the zinc vapor is condensed into the form of a body of molten zinc with the production within the condensing chamber of not more than a negligible amount of blue powder. The vigorous agitating and scrubbing action of the omnipresent molten zinc tends to maintain the temperature in the condenser uniform and thus accelerates the condensation. In general', the con'- denser is operated so as tofmaintain an operating temperature of the order of 550" C. The exhaust animano gases .'l'eaving the icondensing ichaniber V'at' this melamively flow` temperature carry Tthem fssubf'sftantial'ly only `,that amount lof fzinc.EconresponrbI The height lto which moltenzinciis'fnaised"by` the :screw'lift before it`is completely thrown .oii" by centrifugal force depends largely upon .the pitch of the ychannel-like screw and its :speed of rotation. -For example, with lax-inc'h diameter screw, that iis, with the shaft-.like body member m5 -toi t'hescrew :5 inchesin -"diameter, molten Zinc was found to :be `elevated to :a height ci l about 18 Tirmhesavhen the screw Was rotated'sat a fspeedoi :about 5100 .'P. M. .On-the other hand, ianES-inch :diameter screw of substantially :iden-tical pitch, when-motatedat a speed of '300 R. P. M., raisedfth'e molten zinc to a 'height *ofv 24 .inchesal'ongfthe screw.. Both `channel-like screw :liftswere 'of approicimately standard :pitch,'fthat is, the pitch was substantially eqnalfto `the screw diam-eter. vScrew I`lisftshaving 'a pitch 'greater or less than standard .pitch :may be .used with advantage.-

`vTh'ezsingle `spiral channel 22 zshownv 4in 'thedraw fingscalthough Wholly effective, .setsnip iasligl'fit mrrbalfancefdne to Athe .'scoopingV action of .its `iovvermost eend ias it is `moved .through the molten zinc and .tends to causefsome vibration. 'Although this .vibration fisenot prohibitive, itl may be Vcivercome 'fby providing ithe :shaft-like 'body .portion of `the rscreW lift with two lsimilar spiral channels 5180 degrees apart. Such .la idouble .channel is free-ci vibration' :and is extremelyleffective. 'In orderfto .minimize vibration, thel'ower end of the shai-t :may 7befextended below the lowermost endfo'fthe 1 ichannellxsothat it can be :mounted'in a'fsuitab'le `hearing 48.1ocated .in 'the floor of the :condensing chamber as shown in Eig. I3.

The Ioperbtopped channel may be provided `Within the body oi the screw lift rather than eX- Iteriorly thereof. Thus, insteadof the channel l v2.2 being formed as a spiral extending kabout the surface of its shafthke'body member, the channelf-may :be machined in the form oia -U-shape'd fg-roove .50 (Fig. 13) Yor a V-shaped groove 5l (fliig. A14) cut into the .body memben In 'such case, the raxis of the groove advantageously inrclinesdownwardlyand inwardly so zthat .the outer .side :of :thefgfroove Yprovides :the desired retain- .ing wall. ,The open top Vof ysuch :a :groove provides :the-desired retaining Wall opening which permits molten Lzlnc raised by the rotatingy groove to ;bethrownvoutwardly into the interior of the condensing vessel.

If yit is 'desired to minimize'the amount zoi zmoltenzinc maintained inthe bottom 'of the condensing -ch-amber and `yetfinsure an v'adequate `amount of molten metal to be picked up 'by the .screw lift, the bottom ofthe condensing chamber may -be-.provided with `a Well .'52, `as shown -in Fig. vSuch a welljprovidespa substantial 4depth "o`f .molten .zinc in communication with Athe lower end ,ofithescrew-hit-Without requiring this same depth of metal throughout the entire lower'fportion fo :the chamber. The screw lift in vthis modified form fof four :apparatus 'is so .positioned'ras tov extend-:close to Athe `bottom of the Well. -If desired, ,the lower yend V.of the `lift may be mounted in'a :bearing similar to the bearing 48 shown'in IFig.l3.

@Additional-roaming of 'the condensermay be .provided rby l'articial'tooling means. For vex- .a-mpie, a -waterscooledl'shell may. 'be positioned lWithin.Ithec'ondensing :chamber in the `path ofthe .incoming :zinc vv'vapor bearing gasesas described :inkomcoependingrapplication :Serial No. l633'004,

8 -iiledfDecember .5, 1945. YThis internal Vdirect artificial :coolingelement is bathed by .the molten :zincithrown into the condensing chamber by the screw :litand seri/esito Withdraw Iheat both from .the Vmolten:metal and from the incoming gases. '-.lhe artinci'al cooling means 'may :also `comprise -a bayonet-.shaped water-cooled shell immersed 1themolten lzinc Vvin ythe discharge Well t6, as described fin Vour co-pending application `Serial No. 678,540, eie'd :June 22, '1946. In this latterl ityp'e foffdirect fartificial cooling, the cooling element withdraws heatl from the molten metal lin fthefdischarge Well. The violent'a'gitation ofthe imolten imetal within the condensing chamber in.- .sures'the flow-oi? heat from 'the 'body of metal therein .to the metal `in lthe discharge Well and prevents thefexistence of any objectionable tem- :per'ature .gradient therebetween In-the' zinc condensing apparatus shown in Figs. land 7, the zinc vapor inlet vand Waste ygas foutletvaredisposedrsubstantially opposite one another on oppositerend Walls ofthe condensing chamber. -Theiincomingzinc-vapor flows under-the 'depend- ,fing bailie l-35and isgiven ra-Whirling motionwvith'- an Vthe 'chamber "by the rapidly `rotating lscrew lift 2|. The turbulence ,thus produced Within the tcondensing chamberis sufcient to insure an ade- .quate holding time "forthe zinc'vapor to be com- .pletely condensed. The 'holding `time may ,be increased .bytne 'arrangement of yzinc yvapor. inlet and waste'f'gas'foutlet shown in Figs. 8 and`9. It wi1l'be'seen -thatin accordance with this arrangement 'the zinc Yvaporand exhaust-gases are in zt'roduced vvinto and'removed from the condensing :chamber ladjacent opposite fcorners yoi a condens- 'ing chamber "|20 having a substantiallysquare cross-section. 'Infstill another form ci zinc con'- .fd'ens'er useful-.inpracticing our invention, the con- ;densing chamber vIl'has a substantially cylindri :cal :sha-peras shown in Fig. 10. The Zin-c vapor inlet -l l -andfexhaust gas-.outlet i2'rare positioned .fad-j acent'fvonefanother'but 'are vseparated"from 'one another within the condensing lchamber bymeans .of -la vertical baille -53.

Although `the 'zinc vapor inlet H and gas outflet lhavefbeen Ashown in Figs. 1 and 'l as being :shielded gbyba-iles, such nbaffles. Iare not necessary Where the inlet Aandwoutlet lconduits are vsuiiiciently inclinedy to :insure the return flow into'the :condenser of iany :metal "which .may be thrown .into 4these fopenings. '.Thus, as lshown :in Figs. 9 and 11, the vapor supply line 2B andthe gas outfletA I`2 :mayebe Asubstantially vertical yadj acent `their .connect-ion'tothe condenser. Alternatively, the inlet-vor outlet, or both, may communicate With an' obliquely but steeply inclined conduit, suclias "the supplyline '.20 shown yZin Fig. 12, which will insureth'e return flow of molten metal to the )condenser- Thefscrew lift usedin practicing the present Vinvention is `not only highly effective in raising fand throwing 'molten Zincinto the condensing chamber but'itis particularly dependable in operation. The lift extends into the condensing chamber through a single opening in the roei. `'Ihe=stu'ing box positioned Within thereof opening provides an e'iiective'air seal and prevents I'the*orrmition of 'rockoXide yabout tno shaft-litre bodyportion of the 'lift'where it Aenters the con- 'densing chamber. Thescrew lift is thus substantially'free iro'm'fany tendency to bind or freeze during operation land. may be operated continu -ously over anextendedfperiod of time Without interruption. I-fjff'o'r any reason-it becomes nec essary'forfdesirable lto removeithe screwl lift 2i from the condensing chamber, this can be done, in a matter of minutes under favorable conditions, by removing the packing gland 44 and withdrawing the lift through the condenser roof opening 43. The bearings which support the drive shaft 26, being located outside of the condensing chamber, are free from the deleterious effect of zinc vapors and high temperatures and are capable of sustained operation without any precautions other than normal lubrication.

We claim:

1. The method of condensing zinc vapor which comprises maintaining a body of molten zinc within a condensing chamber, raising molten zinc from said body thereof vertically within the chamber and throwing the raised molten zinc by centrifugal force outwardly in the form of an umbrella-like shower into the chamber above the body of molten zinc therein, and condensing the zinc vapor by passing it in a gaseous stream through the chamber in contact with said shower.

2. The method of condensing zinc vapor which comprises maintaining a body of molten Zinc within a condensing chamber, raising molten zinc GEORGE T. MAHLER. ERWIN C. HANDWERK.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 445,096 Theisen Jan. 20, 1891 1,530,154 Gaspari Mar. 1'7, 1925 1,871,657 Bunee Aug. 16, 1932 1,883,665 Fleisher Oct. 18, 1932 2,238,819 Neve Apr. 15, 1941 2,268,219 Lyons et a1. Dec. 30, 1941 Certicate of VCorrection Patent No. 2,457,550. December 28, 1948.

GEORGE T. MAHLER ET AL. It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 5, line 3, for shaft 28 read shaft 26; column 6, line 7, for the Words lower most read lowermost; column 10, line 21, list of references cited, for Bunce read Bunce; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 3rd day of May, A. D. 1949.

[Ilm] THOMAS F. MURPHY,

Assistant omam'aaoner of Patents.

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